The present invention relates to a glass suitable for covering for insulation of electrodes, particularly transparent electrodes of e.g. ITO (indium oxide doped with tin) or tin oxide, and a plasma display panel.
In recent years, a thin flat plate type color display device has attracted an attention. In such a display device, it is necessary to form an electrode for each pixel in order to control the display state in the pixel for forming an image. In order to prevent deterioration of the image quality, transparent electrodes are used as such electrodes. As the transparent electrodes, thin films of ITO or tin oxide formed on a glass substrate, are commonly employed. Here, the tin oxide includes tin oxide doped with e.g. fluorine or antimony.
Transparent electrodes which are formed on the surface of a glass substrate to be used as a display panel of the above display device, are formed into fine lines to realize fine images. In order to control the respective pixels independently, it is necessary to secure insulation among such finely formed transparent electrodes. However, if moisture is present on the surface of the glass substrate, or if an alkali component is present in the glass substrate, it may happen that an electrical current flows to some extent via the surface of this glass substrate. To prevent such a current, it is effective to form an insulating layer between the transparent electrodes. Further, in order to prevent deterioration of the image quality by the insulating layer formed between the transparent electrodes, such an insulating layer is preferably transparent. Various materials are known as an insulating material for forming such an insulating layer. Among them, a glass material is widely employed which is a transparent and highly reliable insulating material.
In a plasma display panel (hereinafter referred to as PDP) which is recently expected as a large size flat color display device, cells are defined and formed by a front substrate used as a display surface, a rear substrate and barrier ribs, and an image will be formed by generating plasma discharge in the cells. Transparent electrodes are formed on the surface of the front substrate, and it is essential to cover the transparent electrodes with a glass in order to protect the transparent electrodes from plasma.
Such a glass to be used for covering electrodes, is employed usually in the form of a glass powder. For example, to such a glass powder, a filler, etc. may be added as the case requires, and then the mixture is formed into a paste. A glass paste thus obtained is coated on a glass substrate having transparent electrodes preliminarily formed, followed by firing to cover the transparent electrodes.
Further, in the front substrate of PDP, if the electrical resistance is too high solely with transparent electrodes made of e.g. ITO or tin oxide, a metal layer of Ag or Al, or of a three layer structure of Crxe2x80x94Cuxe2x80x94Cr (hereinafter, such a metal layer will be referred to as a metal electrode) may sometimes be formed on such transparent electrodes. In such a case, the glass paste is coated also on the metal electrodes, followed by firing.
Such a glass for covering electrodes, is required to have an electrical insulating property, and it is further required that the reactivity with electrodes (such as transparent electrodes or metal electrodes) or with a glass substrate is small, and transparency of the glass layer covering the electrodes, obtainable by firing, is high. Various glasses have been proposed. For example, JP-A-10-316451 discloses a glass for covering electrodes, having In2O3 added thereto in order to suppress reaction of transparent electrodes made of ITO with a glass layer covering the electrodes. The glass for covering electrodes in Examples 1 to 11 of the publication has a composition, as represented by mass percentage, of PbO: 36.0 to 59.5%, B2O3: 17.0 to 25.0%, SiO2: 2.5 to 4.0%, Al2O3: 0 to 2.5%, ZnO: 9.5 to 18.5%, In2O3: 0 to 3.0, SnO2: 0 to 1.5%, CaO: 0 to 5.0%, SrO: 0 to 9.0% and BaO: 0 to 16.5%.
However, in recent years, requirements with regard to reactivity with e.g. electrodes or a glass substrate, and transparency of the glass layer covering electrodes, have become stricter, and it has been difficult to simultaneously satisfy such requirements with regard to reactivity and transparency with a conventional glass for covering electrodes. It is an object of the present invention to provide a glass for covering electrodes which satisfies these requirements simultaneously and a plasma display panel.
The present invention provides a glass for covering electrodes, which consists, as represented by mass percentage based on the following oxides, essentially of:
(hereinafter this glass will be referred to as the glass of the present invention as represented by mass percentage).
The present invention further provides a glass for covering electrodes, which consists, as represented by mol % based on the following oxides, essentially of:
(hereinafter this glass will be referred to as the glass of the present invention as represented by mol %).
The present invention still further provides a PDP having a front substrate, wherein transparent electrodes formed on a glass substrate constituting the front substrate are covered by the above-described glass for covering electrodes.